1. Field of the Invention
The present invention relates to anti-fuses and, more particularly, to a silicide bridged anti-fuse and a method of forming the anti-fuse with a tungsten plug metalization process.
2. Description of the Related Art
Trim elements are devices that are used in analog circuits to provide an electrically programmable method of adjusting certain device parameters. For example, trim elements are often used to trim resistor values in critical circuits. See Corner, “Zener Zap Anti-Fuse Trim in VLSI Circuits,” VLSI Design, 1996, Vol. 15, No. 1, p. 89.
One type of trim element is an anti-fuse. Unlike a fuse which, when programmed, changes from a low-resistance to a high-resistance device to block a current from flowing through the device, an anti-fuse is a device which, when programmed, changes from a high-resistance to a low-resistance device to allow a current to flow through the device.
FIG. 1 shows a cross-sectional view that illustrates a prior-art anti-fuse 100. As shown in FIG. 1, anti-fuse 100, which is formed in a n-type semiconductor material 110, includes a p-well 112 that is formed in material 110, and a n+ region 114 that is formed in p-well 112. In addition, a metal interconnect 116 is formed on p-well 112 to make an electrical connection with p-well 112, while a metal interconnect 118 is formed on n+ region 114 to make an electrical connection with n+ region 114.
In operation, a first voltage is applied to p-well 112 via metal interconnect 116, and a second higher voltage is applied to n+ region 114 via metal interconnect 118. In this situation, the junction between p-well 112 and n+ region 114 is reverse biased, thereby allowing no current to flow from metal interconnect 116 to metal interconnect 118.
To program anti-fuse 100, the reverse biased voltage is increased until avalanche breakdown occurs at the p-n junction. The reverse biased voltage can be increased by, for example, increasing the voltage on n+ region 114. When avalanche breakdown occurs, a breakdown current flows near the surface from metal interconnect 116 to metal interconnect 118.
The current flow causes localized heating which, in turn, causes metal atoms from metal interconnect 118 to migrate to metal interconnect 116 along the path of the breakdown current. The metal atom migration results in a trace of metal being formed along the path of the breakdown current. The trace of metal provides a low-resistance path between metal interconnect 116 and metal interconnect 118. (Prior art anti-fuses can also be programmed with forward-biased voltages that generate the necessary current flow.)
Although anti-fuse 100 performs satisfactorily, there is a need for alternate structures and methods of forming an anti-fuse.